(a) Field of the Invention
The invention relates to a dual working-electrode electrochemical detector. More specifically, the invention relates to such a detector wherein the working-electrodes are disposed in parallel, opposed, closely spaced, relationship.
(b) Description of Prior Art
High Pressure Liquid Chromatography (HPLC) has demonstrated a useful ability to separate large numbers of biologically active compounds in determining measurements of drugs and biochemical concentrations in biological fluids. Electrochemical cells have proven to be both sensitive and selective detectors for HPLC. The cells will typically include a single electrode, however, it has been shown that both the sensitivity and selectivity of the devices can be improved by using more than one working electrode. G. W. Schieffer, Anal. Chem., 52 (1980) 1944, W. A. MacCrehan and R. A. Durst, Anal. Chem., 53 (1981) 1700, D. A. Roston and P. T. Kissinger, Anal. Chem., 54 (1982) 429, and M. Goto, T. Nakamura and D. Ishii, J. Chromatogr., 226 (1981) 33. In the commonest of these arrangements, the cells include an upstream electrode to remove interfering species and a second electrode for the actual measurement.
Work has also been directed toward lowering the detection limits of electrochemical detectors by locating two working-electrodes on opposite walls of a thin layer cell. S. G. Weber, Ph.D. Thesis, McGill University, Montreal, 1979. This concept was first developed by Reilley and co-workers for stationary solutions, L. B. Anderson and C. N. Reilley, J. Electroanal. Chem., 10 (1965) 295. L. B. Anderson, C. N. Reilley, J. Electroanal. Chem., 10 (1965) 538. L. B. Anderson, B. McDuffie and C. N. Reilley, J. Electroanal. Chem., 12 (1966) 477 and C. N. Reilley, Pure Appl. Chem., 18 (1968) 137. Fenn et al extended this to flowing streams with only limited success. R. J. Fenn, S. Siggia and D. J. Curran, Anal. Chem., 50 (1978) 1067. For a discussion of the results of this see also Daryl A. Roston, Ronald E. Shoup and Peter T. Kissinger, Anal. Chem., 54 (1982) 1417 at page 1434 which also describes the redox (reduction-oxidation) cycling using parallel-opposed dual-electrodes. As can be seen in Roston et al, the Reilley et al results are not described as too promising.